html {
    background-color: black;
    background-image: url('http://image.naldzgraphics.net/2012/04/6-r12-3.jpg');
    background-size: cover;
    background-attachment: fixed;
}

 .page-header {
    background-color: #FFFFFF;
    color: white;
    padding: 20px;
}
.gallery {
    background-color: purple;
    padding: 1px;
    width: 700px;
    margin: 0 auto;
    margin-top: 30px;
    text-align:center;


    background-color: black;
    border-color: purple;
    font-weight: bold;
    display: inline-block;
    padding: 5px 10px;
}

.main-menu a:hover {
    background-color: purple;
    color: red;